To ensure proper functionality of the on-board power network of a motor vehicle, determination of the capacity information relating to the on-board power network battery is of great importance to operate the battery under an optimum charging and discharging strategy. For conventional motor vehicles having only a single on-board power network and typically a lead-acid battery with a nominal voltage of 12 volts, the capacity information is determined by measuring a battery current, a battery voltage, and a battery temperature. Because such on-board power networks are fed by way of a claw-pole generator that generates a current ripple in the on-board power network, the excitation of the battery due to this current ripple can also be utilized for purposes of determining the capacity information.
This option of determining the capacity information is not deterministic, however; in particular it depends on the power draw and output of the claw-pole generator and on the users and cabling of the on-board power network. In electrically-driven motor vehicles, and/or vehicles having multiple on-board power networks coupled by way of a DC converter, sometimes there is no claw-pole generator in the on-board power network because the battery is dynamically fed by the DC converter. A current ripple, which can be used to determine the capacity information, is consequently not present in such on-board power networks.
From DE 10 2014 007 016 A1, a method is known for determining a status information that describes the charge state and/or the capacity of a first electrical energy storage device, wherein the first electrical energy storage device is connected in series to a second electrical energy storage device. Here, a defined amount of electrical energy is introduced from the second energy storage device to the first energy storage device, whereupon a variable state parameter of the first energy storage device is determined as a function of the amount of electrical energy introduced, and the status information is determined using the state parameter.
DE 10 2013 219 293 A1 discloses a vehicle with a high-voltage on-board power network, a low-voltage on-board power network, a DC chopper between the two on-board power networks, a low-voltage energy storage device in the low-voltage on-board power network, and a high-voltage energy storage device in the high-voltage on-board power network. Here, when the vehicle is in a stance phase (for example, standing or waiting while idling), the low-voltage energy storage device can be loaded at a pre-definable current pulse by the DC chopper, and the current response to the current pulse can be measured using a battery sensor associated with the low-voltage energy storage device.
The features and advantages of the present embodiments will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.